Safer Shiftwork Through More Effective Scheduling

Oct. 4, 2006
A new program from the Liberty Mutual Research Institute assesses worker injury rates based on work scheduling factors.

So many industries utilize shiftwork schedules that nearly 15 million full-time workers in the United States work shifts outside the traditional 9-to-5 or flex-time workday, according to the Bureau of Labor Statistics. Yet those added shifts, implemented specifically to increase profitability, actually may be costing companies money through higher worker injury rates.

By rethinking how you schedule shiftwork, you can help keep workers safe and make each shift more effective.

Based on the findings of a recently published Liberty Mutual Research Institute study modeling the impact of the components of long work hours on injuries and accidents, the loss prevention group developed a program to assess worker injury risk based on such work scheduling factors as time of day, hours per shift, number of consecutive shifts and time between rest breaks.

The program addresses the following shiftwork problems:

  • Work-related injuries increased 15.2 percent on afternoon shifts and 27.9 percent on the night shift relative to the morning shift.
  • Injury risk increases nearly linearly after the eighth hour of a shift, with risk increasing 13 percent on a 10-hour shift and almost 30 percent on a 12-hour shift.
  • As consecutive shifts increase, injury risk also increases, but at a higher rate for night shifts than for day shifts.
  • Average risk for injury is 36 percent higher on the last night of a four-consecutive-night shift. Risk increases incrementally over each night on the job: 6 percent higher on the second night, 17 percent higher on the third night culminating at 36 percent on the fourth night.
  • Injury risk is 2 percent higher on the second morning/day shift, 7 percent higher on the third day and 17 percent higher on the fourth day than it is on the first shift.
  • Injury risk also increases as time between breaks increases. The last 30 minutes of a 2-hour work period has twice the risk of injury as the 30 minutes immediately after the break.

Combating the Problem

One way to combat these problems is to evaluate the combined effect of work scheduling factors rather than to just limit total work hours. For example, scheduling four, 12-hour day shifts with hourly breaks will produce less risk than six, 8-hour night shifts with hourly breaks. Both shift schedules add 8 hours of work, but only one has significantly less risk of injury.

If you are contemplating adding overtime or expanding shifts, several guidelines will help you build a safer shiftwork schedule. For example, establish maximum limits for days and nights worked per week, including overtime. Whenever possible, favor day/morning shifts over afternoon or night shifts. Keep schedules regular and predictable, and alternate weeks of overtime with weeks of normal time.

Consider adding hours to existing shifts or add an additional day of work to the project, and limit work to five or six consecutive shifts. Provide for frequent rest breaks. Hourly breaks generally are appropriate, but consider providing more frequent breaks for highly repetitive or strenuous work.

Schedule work so every worker has at least two consecutive rest days and at least one of these days is Saturday or Sunday. Avoid scheduling several days of work followed by four- to seven-day mini-vacations. These schedules should be used only when there is no other choice, such as in mining or oil exploration.

For those situations when you have to schedule night shifts, here are some ways to help combat the increased risk of injury:

  • Keep consecutive nights shifts to a minimum four nights maximum in a row should be worked before a couple of days off and schedule no more than 48 hours of night shiftwork per worker per week.
  • Educate workers on the importance of getting enough good sleep. Suggest they use black-out drapes, turn off phones and pagers and use a fan or white noise to mask daytime noises. Regular exercise, diet and relaxation techniques also are effective strategies for coping with night work.
  • Consider alternatives to adopting permanent night shifts. Most workers never fully adapt to night shiftwork, since they go back to a daytime schedule during days off.
  • Avoid quick shift changes and adjust shift length to the workload.
  • Take into account all aspects of workers' job and home lives when changing work schedules.

When scheduling shift rotation, provide a minimum of 11 hours off between shifts and a minimum of 24 to 48 hours when rotating workers off the night shift. Ideally, the change from the night and morning shifts should happen between 7 a.m and 9 a.m., as starting the morning shift too early often cuts down on evening sleep time. Also keep in mind that forward shift rotation going from a day to afternoon or afternoon to night or night to day shift is more compatible with normal sleep patterns than backward shift rotation.

Involve Workers

Whatever approach you take to scheduling shiftwork, a very important component is worker involvement. You should solicit worker feedback in the scheduling process rather than handing down a mandatory schedule. Provide training or awareness programs for new shiftworkers and their families to help them cope with the irregular schedule. Lastly, ensure that workers on all shifts including the non-traditional schedules have access to health care and counseling services.

With 15 percent of the total full-time U.S. work force working non-traditional shifts, rethinking shift scheduling can make a significant impact on productivity and worker safety.

Sidebar: Do Extended Work Schedules Lead to More Injuries?

Limited employee involvement in schedule selection, long workdays and an excess of consecutive workdays all are linked to increased risk of ergonomic-related injuries, according to a report published by Circadian Technologies Inc. Poor work/life conditions and sleep deprivation also can lead to ergonomic injuries and lost workdays, especially among employees in extended-hours positions (regularly working outside the hours of 7 a.m. to 7 p.m.).

"We have long known that long work hours, high fatigue levels and work schedules that fail to account for human physiological needs are linked to a 20 percent increased rate of workers' compensation claims among facilities with extended-hours operations," said Kirsty Kerin, Ph.D., one of the principal authors of "Ergonomics Risks, Myths and Solutions for Extended Hours Operations."

Kerin's report further details the link between work practices and ergonomic injuries, such as musculoskeletal disorders (MSDs). The study notes:

  • In a survey of more than 12,500 extended-hours workers, 30 percent of male workers and 41 percent of female workers reported chronic or frequent back pain, while 16 percent of male workers and 27 percent of female workers reported chronic or frequent wrist pain.
  • Sleep deprivation could possibly be damaging in terms of muscle, ligament or tendon injury. With the average extended-hours employee sleeping only 5.1 hours to 5.5 hours each day when working a night shift, they could face an increased risk of ergonomic injuries.
  • The balance of work and home life is important in controlling the number of lost workdays due to MSD complaints. Both men and women who face simultaneous presence of high mental workload and increased domestic workload have increased neck and shoulder MSDs.
  • Disturbances in sleep affect pain and negatively impact the time it takes a worker to return to work after suffering a soft-tissue injury such as low-back pain.
  • Six days of restricted sleep (4 hours per 24-hour period) caused changes to the sleep architecture that are similar to the changes seen in people suffering from depression. Also, lack of sleep causes changes in several natural body rhythms of hormone secretion including melatonin, cortisol, thyroid-stimulating hormone, leptin, prolactin and growth hormone.

In addition, researchers found that although working more than 8 hours a day was shown to increase ergonomic injury rates, working two to four weekends a month also was shown to have a negative impact. Since most 12-hour schedules limit consecutive workdays to four, and provide employees with twice as many weekends off as 8-hour schedules, there are pros and cons to each schedule type and 12-hour shifts are not inherently problematic.

"Involving employees in schedule selection, training workers on managing the work/life demands of working extended hours and revisiting workplace policies such as break rules and rest periods can significantly decrease the risk of costly accidents and injuries," states Alex Kerin, Ph.D., the other principal author of the study. Fatigue management initiatives to decrease employee fatigue while at work and commuting to the job as well as to improve sleep quality also represent critical interventions for extended-hours employers, Kerin noted.

George Brogmus is technical director, ergonomics, for the Liberty Mutual Group's Business Market, and Wayne Maynard is director, ergonomics and tribology, Liberty Mutual Research Institute for Safety (

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